Gilly, the car will benefit from breathing mods yes. But from what we are led to beleive, the operating window of the ECU is very limited. So you add more air, you need more fuel. Well the car is very clever, and it knows for the revs and engine load, what fueling it should give (this has a window dependant on other things too), so once you hit the upper window in any given situation you wont get any more power as the car will simply not give it any more fuel, so it runs lean. This coupled to a FBW throttle can control the intake too, thus controlling the airflow. SO yes you will get gains, but only up until the point the car doesnt know what to do with the extra breathing which is pretty quick.
From the technosquare website (these guys map loads of 350z, so generally know their stuff I am led to beleive!)